Mixed fiber felt



March 1, 1969 T. c. DuvALL MIXED FIBER FELT Filed oct. 19, 1953 o m o 6 0 8 N. 6 m@ w HB G 5 TE N s. 6W E E N r cw. PLTLNNIO 5 c i 4 C (I, f -|I|| l I l IIIJIIIIIIIIU-IIIM o y u w a Fey] 2,926,417 MIXED FIBER FELT Thure C. Duvall, Cinque-t, Minn., assignor to Wood Conversion Company, St. Paul, Minn., a corporation of Delaware Application October 19, 1953, Serial No. 387,013 6 Claims. (Cl. 28-78) The present invention relates to fiber felts and felt bases, and in particular to dry-formed unbound felts having a mixture of relatively long fibers and relatively short fibers, all useful per se and as raw material for added binder or bonding treatment.

kLong fibers of the kind generally referred to as textile' fibers are variously individualized from masses thereof by mechanical combing or carding in such a way that individualized fibers may be taken up in air to form steady streams of substantially uniform content. Many kinds and combinations of machines are available. One disadvantage is the low capacity of such machinery for its bulk and its investment cost.

Short fibers, such as those ultimate fibers derived from wood, have no value as textile fibers when used alone, and may not be used as felts unless bound fiber to fiber. When so bound, the felt has undesirably low strength at low density, as in flexible insulation and cushioning felts, and greater strength as the density increases, as in rigid insulation board, cardboard and paper.

The said low-density bonded fiber felts are lacking in high tensile strength because of the shortness of fibers and the greater spacing of bonds. However, integral fiber bodies composed of short fibers such as from wood, are in use extensively because of the relatively greater capacity of equipment to handle such fibers, when compared to the textile fiber field.

Although it is a simple idea that such a short-fiber product may be strengthened by incorporating longer or textile fibers throughout it, this has not been commercially accomplished with retention of the low cost of production applicable to the short-fiber field.

In this description and in the claims the terms long fibers and textile fibers signify those natural or synthetic fibers other than those of wood having length which enables them to be spun to form threads having useful strength without use of binder or adhesive in the thread. The terms short fibers and non-textile fibers include all fibers of wood and other fibers having such lengths as preclude spinning them to threads having useful strength without use of adhesive or binder. In general, the authorities give a length of 5.08 mm. (.2 inch) as the lower limit of length for making economically useful spun threads (see Matthews Textile Fibers, 1947 ed.,

page 27). There are a few wood fibers having lengths in the range from to 7 mm. as follows:

Grand fir 5.0 Douglas fir 5.0 Western larch 5.0 Southern yellow pines 4 to 6 Sitka spruce 5.5 Bald cypress 6.0 Redwood 7.0

These as well as all the shorter fibers of wood are not economically spinnable. Hence, all wood fibers are included herein as short fibers. In the present invention, wherein short fibers are mixed with long fibers, it is to be understood that the latter are so chosen as to be longer than the former, even though the definitions as given would otherwise permit the reverse relation.

In my copending prior application Serial No. 276,150, filed March l2, 1952, subsequently abandoned, of which the present application is a continuation-in-part, there are described numerous ways by which air-laid dry felts Yce ' it has been the objective to make felts of mixed long and short fibers by use of Vfber-dispersing and felting processes commercially suitable for one but not the other of such long and short fibers.

The object of the present invention is to produce an air-laid dry fiber felt having fibers consisting of mixed long and short fibers but in a limited range of admixture in order to secure maximum benefits from the mixture.

It is a general object of the invention to provide an air-laid dry felt of fibers consisting of 20 to 80 parts of long fiber to to 20 parts of short fiber.

It is a particular object of the invention to provide an air-laid dry fiber felt having 20 to 80 parts of long fiber cotton to 80 to 20 parts of wood cellulose fiber.

' It is an object of the invention to produce open and porous low density dry-formed mixed fiber felts of the kind described, and to introduce fiuid binder material into the felt for treatment to form bound felts.

It is an additional object of the invention to provide bonded felts which are the air-laid felts of the foregoing objectives to which dry binder has been added before or after felting, and only activated to adhesiveness within the felt, with or without compression of the air-laid felt.

Various other and ancillary objects and advantages of the present invention will become apparent from the following description and explanation of the invention, given in reference to the accompanying drawing in which:

Fig. l is a plot of property values over the entire range of admixture of long and short fibers.

Fig. 2 is a general vertical sectional view of apparatus by which the product may be made.

Largely because textile fibers are more costly as raw material and more costly and slower to handle-mechanically in forming air-laid felts, all relative to wood fiber, it has become an important objective to combine the two fibers in air-laidfelts with substantial retention of the desirable properties deriving from textile fibers and substantial retention of the lower cost and` greater capacity Vin operations with wood fiber. The product of the present invention meets those objectives.

In using given equipment to make a range Yof felts varying in composition from long fibers to 100% short fibers, the product derived varies in density and thickness. For comparison of properties, one variable must be fixed. In presenting property variations for explaining the present invention, the weight of material per unit area is held substantially constant as will appear in Table I below. This value is not dependent upon the properties of the mixture, but upon the fixed rates of feed of material and of operation of the apparatus.

In Fig. l there is shown a plot of property values of a series of felts made from l-inch staple cotton ber and sultite wood cellulose. The mixed dry fibers individualized in a moving stream of air have been felted on a cylinder by a continuous procedure hereinafter described, and the felts evaluated. Fig. 1 is a plot of evaluations from the following T able I. A.

In Table I, the columns are numbered. In full, the columns are:

Col.1. Percent by weight of cotton (remainder wood fiber). 4

Col. 2. Thickness in inches.

Col. 3. Density in pounds per cu. ft.

Col. 4. Weight of mat in pounds per 1,000 sq. ft.

Col. 5. Tensile strength in direction of web, measured in grams pull to maximum load on 1 inch width.

Col. 6. Tensile strength across web (units as in col. S).

Col. 7. Stretchability in percent, to maximum load, in

direction of web.1 i

Patented Mar.` 1, 196() Col. 8. Stretchability in percent, to maximum load across web.

Col. 9. Compressibility to one-third original thickness, in pounds per sq. ft. C`ol`.102 Percent of original thickness recovered on 1mrnediate release from test for col. 9;

Table l 1. 87 75 8. 0 15. 7 18.1 24. 5 245 87. 5 1. 82 78 9.0 2U. 0 22. 0 26. 4 180 90. 6 1.60 73 10.3 23.3 22 2 29 8 156 88 7 1. 26 70 4. 7 30. 3 2S 6 32. 4 99 94. 0 1.14 72 5 3 32. 3 28. 9 38. 2 02 90 9 98 73 5. 0 30. 7 32. 0 32. 8 48 V88 3 0. 97 75 5. 7 36. f) 30. 0 3B 7 (il 95. 2

Fig. 1 shows that the properties of the 100%-cotton felt are little changed by inclusion of wood fibers up to about. 20% content. At this point' the compression value on line 10 (col. 9 of Table I) begins to improve, and the strength across the web, on line 11 (col. 6 of Table I), begins to drop. The compression improves only gradually and after 60% wood ber it rises with accelerated loss of strength in curve 11, but with a beginning of increase'in strength with the web, as on line 1-2 (col. 5 of Table I).

As the percentage of wood ber increases above 60%, boththe compression values on line 19 and the tensile strength values on line 12 increase up to 80% of wood fiber, at which point the tensile strength curve 12 begins a sharp drop. But these values alone are not disadvantageous above 80% of wood ber, being higher than theirr values from 0 to about 65% of wood ber. The said drop of values in curve 12 is accompanied by an acceleration in the drop of curve 11, the slope of which passes through the 45 angle atabout 80% of wood ber content'.

The plot shows an optimum combination of values in the range between dottedy lines 13 and 14, which are taken as the limits for the present invention.

A mixed fiber felt may be formed by a suitable deposition of fibers from an air suspension of a mixture of individualized long fibers and short bers. Mixing and individualizing the fibers may be effected invarious ways. To maintain individualization theV air suspending the bers must be kept in motion. Felting may be accomplished in numerous ways. out of the air as in gravity deposition, but the formed feltis of such low density that it must be compressed before it has strength enabling it to be handled or moved from its support.

The practical process is to felt by ltering on a foraminous member such as a wire screen, and to havethe screen move continuously through a deposition area. This permits the continuous formation of a web of which every cross-severed portion is alike. By virtue of' such continuous formation, there is an inherent unidirectional character to the structure and its properties. These are reected in the properties graphed in Fig. l, wherein the tensile strength across the web direction is greater than in' the-web direction. This signifies that long bers tend to lie crosswse of the web. Hence; asA the proportion of; long bers decreases', the strength across the we should decrease, as shown by line 11.

Fig. 2 represents for the purpose of illustration one way in which the described felt may be formed. Numeral 20 represents an infeed ductvv for air and undispersed short-ber material. The duct 20'enters into a side opening 21 of a cylindrical housing 22 in` which is a high speed rotor,. consisting of numerous. spacedV plates 23 on axle 24. To and between adjacent plates 23 are mounted swinging hammers or blades 25 which just' clear the interior of housing 22 in rotation of the rotor. An arcuate portion of the cylindrical housing 22 The fibers may be allowed to drop is perforated as shown at 27, over which is a crescent shaped (in cross-section) collecting hood 2S, leading to a discharge nozzle-like conduit 29. High speed rotation of the rotor causes a fan-like action, drawing in air at 20 and discharging air at super-atmospheric pressure in conduit 29. The fibrous material is individualized, and individual fibers passthrough the perforated section 27;

The disperser above described is a type unsuitable for long or textile fibers, and extremely suitable for handling wood fibers at high capacity. The resulting stream of air carrying wood fibers in conduit 29 is used to doff textile fibers carded onto any conventional or special lickerin roll or carder of the textile industry.

All illustrative form of carding device is shown in functioning relation to the nozzle 29. It consists of a carding cylinder 30 with teeth 31 for carding textile material 32 suitably fed to it at a space between the top of top wall 33 of conduit 29 and a feed roll 34. The carding is effected at a level near and preferably below the center of lickerin roll 30, so that the carded textile bers are brought downwardly to the lowermost portion of the roll 30, to be dofed by the stream of air and fiber from conduit 29. For this purpose the lower wall 36 of conduit 29 slopes upwardly to a narrow dofiing zone 37.' The narrowing of Conduit 29 to the dofng zone increases the velocity of the dofling stream to enhance its dofiing action. By this procedure, uniformly fed textile material 32 is dispersed and uniformly mixed into the short fiber material, also fed at a uniform rate. By control of rates of feed and operation, the proportion of long and short fibers may be controlled for uniformity over a long period of continuous operation.

The mixed stream of fibers is housed in a duct 40 leading to a deposition area on a continuously moving foraminous conveyer. Although the duct 40 is shown as flaring, this is not essential, where the deposition area is larger than the cross-sectional area of the doing zone. As shown, the mixed dispersion 41 expands from the dotiing zone 37 to the deposition area indicated. This expansion causes bers to move apart relatively, lessening the opportunity for them to fiocculate, whereby individual fibers rather than fiocks are deposited. It is to be understood that the stream 41 of mixed fibers may be produced in other ways, for example, by feeding both the textile sheet 32 and a wood ber lap to the carding device.

The foraminous conveyer may be of any continuous type, and as shown is a cylindrical screen 45 of the character shown in U.S. Patent No. 2,451,915 to Buresh. Cylinder 45 turns at a controlled rate on axle 46 with its surface against the end of conduit 40. Within the cylinder is aduct 47 which is in effect a continuation of duct 40.and which extends dametrically'of cylinder 45 to an outside duct 4S, effective as a continuation of duct 46. Duct 48 leads to exhaust or to a suction device, which latter may be operated to augment and control the effective differential pressure under which the fibers form the felt 50, shown as lifted from cylinder 45.

The unbonded felts produced as described are very fiexible, of low density and suitably strong, beingy useful` per se, as for cushioning and insulation purposes. The" felts may be greatly strengthened and changed advantageously in many properties, with and without compression. There may be present in the felt dry binder material whichvi's activatable to adhesiveness as by subjection to heat, or high humidity, or vapo'rs of absorbable solventlike materials. Such binder may be present at the time of felting or added after felting. It may be a coating on either the short bers or the long fibers, or some of such bers may consist of such binder material, for example, celluloseA acetate. It may be a powder mixed into the stream of mixed fibers, so that it is lodged in the felt as formed. Such practice, however, involves passage of some of the binder through the filter, wherefrom it may be recovered.' However, to 'effect a controlled'compositionfof liber and of binderl so added, mo're complicated equipment is required.A

.It is, therefore, preferred to add binder'after the felting. Solid binder. may be dusted or'worked into the felt, or carried into it by an air stream. Such non-liquid binders-are activated according to their character, for example, thermoplastic or thermosetting po'wders, coatings, or bers, are activated by heat, with or without compres? sion of the felt.

`Liquid binders may be impregnated into or sprayed into or onto the dry-formed felt. For example, a single thickness of the formed felt may befmoved in contact with a roll bearing the liquid, to coat and impregnate the felt. v The felt may pass through the nip of two rolls andi through a pool of the liquid adhesive located in the nip, on one or both sides of the felt. Av single thickness of feltpassing lover a suction area may be sprayed with liquid adhesive to load the interior with binder, followed, if desired, by further distribution by rolling and compressing. Still' another "way is to bring two webs together to form one, and to spray adhesive into the interfacial regian, or to precoat the combining faces, followed by rolling compression to` spread and distribute the applied liquid. According to' the liquid, the setting of the adhesive' may vary. For example, latex emulsions need only to be dried, or dried and cured. K

When binder is added, the property lvalues may be without binder, must be mechanically handled and moved to effect their impregnation, and it is in these stages of manufacturing bound felts that the strength values are important. Dry unbound felts having from 0 to 80% of sho'rt fiber are readily carried to and through the impregnating steps, but above 80%. of short fiber, the small amount of long fiber is insuicient to permit continuing a process through steps to add liquid or dry binder as described. Y

The following Table II evaluates bound mats of sulfte fiber and cotton waste, made as described, and then impregnated with an aqueous suspension of synthetic elastomer solids, effected by various dilutions of commercial latices having about 50% of solids.

The impregnating latexV dilution may contain antioxidant agents for the binder to add to the permanence of the bound felt. It also may contain water-soluble wetting agent to accelerate the rate of impregnation of the felt by the liquid suspension. Where the impregnation is-carried on continuously in a line including the felting apparatus, such as exemplified by Fig. 2, the amount of wetting agent in the liquid may be varied for each particular impregnating apparatus, so that the impregnation may be timed for the speed of fo'rmation of the felt.

The impregnated felt may be compressed to various densities before heating, drying and curing the binder, thus to form mats of various densities as illustrated in Table II.

Table II Percent Fiber Lbs. Bound Bound Tensile Strength in Latex at, at, pounds per inch of Sample S-677 solids Density Weight width Cotton per 100 in lbs. in lhs. Sultte Waste lbs. per en. per M Fiber ft. sq. it. Width Across varied greatly by the proportion of binder to fiber, the kind of binder, and the density at which binding is effected. These effects greatly outweigh the significance of proportions as charted in Fig. l, so that in bound felts the component parts may be outside the range between lines 13 and 14. But practically, the felts formed as described The invention is not limited to cotton as the long fiber. Wool, jute, reclaimed tire cord and others may be used. Where latex, such as that described above, is used in the products of Tables II and III, its bond increases on aging, as indicated by values in Table III. Table III also shows use of other combinations of short and long fibers.

Table III Bound Mat Tensile Strength in lbs. per inch width Unbound Mat-Fiber Com- Lbs. Sample 8.677 position Latex Thick- Pounds Pounds Before Aging A fter per ness. per eu. per M Aginglbs. Inches It. sq. It. Aver. Fiber Width Across Aver.

0l aso f.legw o 0.103 s. 9s 77 o. ao o. 6o o. 45 0.13 331 {7% Smm me 2 o. 09o 11. 5 se 1.2 o. s 1.1 1 11 1a. 5 0.103 11.7 10o 1. 3 2. 3 1. s 3. 2e

14. 9 0.141 7. 32 se 2. 7 2. 9 2. s 2. 7s 40% Wool Napper Flock.. ggg sume Fb 26. e o. 079 1s. 7 11o 16.2 21. s 19. o 2. 5s 30% Fiber 40% Cotton Thread Waste 7. 1 0. 117 7. 28 71 1. 1 1. 6 1.4 1. 34 0'7 Cotton Nspper Waste {ggj Cyttf; llread Waste s. o o. oas s. es 2s o. 75 o. 7s 0.77 o. e3 {ggg} tfglllgre-Wi-- s. 7 o. 052 e. es ao o. 7s 1.00 o. 87 1. 74

Webs 1 of the-present invention arezsuiciently strong to permit couching--in-a=horzontal'direction as an un.--

supported spanfrom onecarrier tot-another,- as for: ex-

ample, from one endless-belt.dischargingthe web from its formingv equipment to another endless belt, such as one openmesh wirescreen: to carry' it through liquid impregnating equipment.

The invention is not: limited to vthe exemplary1embodiments herein given, and it is contemplated that numerous changes may be made within the-scopeI ofA thev invention expressed in the' appended claims;

Il claim:

1. An air-laid felt inztheform of.` apiece ocontinuously formed web characterized by uniform diferencesl in structure and propertiesvin right'` angular directions respectively'with and acrossv the` direction offormation of the web,- saidweb comprising a felt* of fibers. extend-- ing generally in different.4 directionsxwhich fibers consist of individualized long fibers andi individualized short fibers, said long fibers beingY stapleI cotton fibers having a length of at least 5.08 millimeters, andv saidshort fibers being wood fibers from which substantially all the lignin has been removed by chemical digestion, which wood fibers areshorter than said long: fibers anrihave` lengthsv not greater than7 millimeters,.therlong. fibers being present by weight in amount from 20:to; 80 parts to 8.0 toA 20- parts of short fibers, said felt having. a greater tensiley strength in one of said directions than in the other.

2. An air-laid felt in the form of a piece of continuously formed web characterized by uniform diferencess in structure and properties in right angular'direc'tions respectively with and across the: directionof formation ofy the'web, said*webacomprising'a-felt of fibers extending generally iny different: directions: which. fibers consist. of individualized long fibers and. individualized shortv fibers,v said; longv fibers. being stapley cotton. fibers having a length of at least 5.08v millimeters, andzsaidshort fibers4 being sulfite'cellulosewood fibers and shorter than said long fibers and having lengths not greater than 7 millimeters, the long-fibersbeing. presentl by weight in amount from 20 to 80 parts to 80 to 20 partsv of short. fibers,vv

said felt having a greater tensile strength in one of said directions than in the other.

3. A felt' according to claim 1 inrwhichA the fibers are individually free exceptfor their interfelted relation.

4. AI feltaccordinggto claim 21in` which the fibers arel individually free except for their interfelted relation.

5.v A felt according to claim 1- infw-hichfthe fibers are.

bondedv one to. another.

6. A felt accordingto-claiml in which thefibers are bondedone vto another. 

